Any advice on window boxes?

[HotSprocket]

Apologies in advance for what may be an idiotic question.

Does anyone know if it's possible to fit window boxes on a window ledge that isn't flat? The ledge is small and slopes down from the window. I could tie them on somehow...or is that a really stupid idea?

My friend has his heart set on window boxes and i wanted to buy him some but he has rubbish window ledges!

You can get brackets. Don't know where from but I've seen them on windows

Oh good, i thought i might be able to get something like that. I'll go on a search.

Thanks